This invention relates to imaging of materials by X-ray Computed Tomography (CT) and Nuclear Magnetic Resonance Imaging (NMRI), and more particularly, relates to imaging of materials to determine mechanical and petrophysical properties of such materials.
Traditional studies of rock compaction have used measurements of fluid expulsion and axial shortening of a sample to measure compaction and dilation behavior of such a sample. Athough much can be learned from these measurements of average bulk properties of a sample, they do not reveal how physical properties vary spatially within a sample. Laboratory measurements of rock properties may result in nonuniform compaction throughout a sample, so that the average strain at which a sample fails may be considerably different from the local strain at the location of any first failure.
Moreover, many rock samples are intrinsically heterogeneous, even on a small scale, and the behavior in each such region of the sample may be of interest. For example, in studies of the compaction of turbidite earth formations, the turbidites are composed of thinly laminated and interbedded sands and shale having an overall thickness of from a few millimeters up to a few feet. Measurement of the separate bulk compressibilities and Poisson's ratios of the sands and the shales in the turbidite sequence is necessary because any hydrocarbons are normally contained only in the sand fraction of a turbidite reservoir.
In other mechanical deformation studies, there may be a large local variation in sample properties combined with the need to be able to make non-invasive measurements without altering the sample. An example of such a study is brittle failure in unconsolidated sands, where the sample cannot be removed from its compaction cell to examine any fracture after brittle failure because the sample becomes unconsolidated without confining stress.
Such mechanical deformation studies may generally be conducted to determine the strength of a particular material. For petrophysical applications, such studies may be employed to determine reservoir subsidence or compaction characteristics and thus aid in the design of production platforms or any recovery process used at a particular location of a reservoir.
There exists, therefore, an unfulfilled need to make local, non-invasive measurements of the mechanical properties of a sample, such as bulk compressibility and Poisson's ratio, and to study failure mechanisms for such samples without removing the sample from mechanical deformation apparatus.
These and other limitations and disadvantages of the prior art are overcome by the present invention and methods are provided for studying in a non-destructive manner the local changes in mechanical and petrophysical properties during material deformation.